Air Venturi Valves open an air line into the jet stream which pulls in air bubbles, so that you can increase/decrease the pressure of that jet and inserts bubbles into the flow.
Water Diverter Valves diverts the flow of water from one jet zone of the spa to the other.
Looking from the outside of the shell, if the piping goes straight down, this is a Venturi Valve. If the piping goes to a "T" shape, this is a Diverter Valve.
Waterfall Control Valves are the larger size and have a higher profile